1. Field of Invention
The present invention relates to an hydraulic latch for a small diameter tubing string suspended beneath a wellhead and, more particularly, but not by way of limitation, to a system for and method of selectively securing and, when necessary, releasing capillary tubing suspended in a well bore in a manner affording automatic release in an emergency situation to maintain the reliability of a subsurface safety valve through which the suspended tubing passes.
2. History of Related Art
A modern practice in the oil and gas industry is the use of small diameter tubing to deliver select chemicals down a well bore. Typically, devices are used at the wellhead to confine pressure in the well around the tubing suspended therein. By using such techniques, the production rates from natural gas wells, otherwise adversely affected by corrosion and the buildup of such substances as scale, paraffin and salt, can be improved. Prior to such innovation, producers traditionally treated the wells by inserting chemicals and soap sticks at the wellhead and relying on gravity to carry the treating agent down the well to where it was needed. However, with small diameter tubing inserted into the well, the treating chemical may be pumped down the well. Such tubing is generally referred to as capillary tubing, which is usually ¼, ⅜ or ⅝ inch in diameter. The chemical is pumped under pressure down the capillary tubing and allowed to enter the well where it can do the most good. A check valve at the lower end of the tubing controls the release of the treating chemical and prevents well pressure from escaping up the capillary tubing.
Current wellhead systems taking advantage of capillary tubing techniques generally utilize packoffs for controlling the capillary tubing being inserted at the wellhead. There are many varieties, but one system is set forth and shown in U.S. Pat. No. 6,955,225 issued Oct. 18, 2005, assigned to the assignee of the present invention. This patent illustrates control mechanisms for capillary tubing securement as well as means for quickly regaining control of tubing within a wellhead that has, for one reason or the other, not been secured by conventional securing systems. Reliability and safety are integral elements of an effective wellhead system. Other critical aspects of the wellhead system include the ability of the wellhead equipment and systems to prevent the uncontrolled release of gas, hydrocarbons, and/or other products from within the underlying wellbore in the event of an emergency. Emergencies can occur through natural disaster, sabotage, breakdown in equipment, and/or related events which cause an interruption in the existing securement or sealing system of the wellhead and/or wellbore.
The prevention of a blowout is so critical that safety valves are disposed downhole. Such safety valves are disposed within the borehole to facilitate an automatic sealing of the borehole in a manner for getting the release of gas, hydrocarbons and/or other substances within the borehole that are typically under pressure in the event of such an emergency. The problem exists with such downhole safety valves when capillary tubing and the like is suspended down the wellbore. It can be readily understood that a valve would be unable to seal effectively if tubing were extending therethrough. In such an event, the absence of effective valve sealing would most likely result in the release of the gas and/or hydrocarbons due to the fact that the integrity of the sub-surface safety valve has been compromised.
For the above-mentioned reasons, a reliable method of and apparatus for tubing release above a sub-surface safety valve is greatly needed. Such a method and apparatus must be of the type that can be quickly activated with reliable effectiveness in the event of an emergency. The present invention provides a means for and method of quickly releasing tubing within a borehole above a sub-surface safety valve without the need for operator intervention. In this manner, sabotage, natural disaster, or other unforeseen emergencies at the wellhead can result in the release of the tubing that stands to potentially interfere with the sub-surface safety valve therein providing a fail-safe mechanism to seal off a borehole in such an event.